Most lubricant base stocks, including most of API Group I to Group IV fluids, have viscosities at 100° C. in the range of about 4 to about 6 cSt. When these base stocks are used to formulate different viscosity grade lubricants it is necessary to blend them with high viscosity base stocks. Currently, the readily available high viscosity base stocks include bright stock, high viscosity polyalphaolefin (PAOs) and polyisobutylene (PIB).
Bright stock and PIB have poor viscosity indices (VIs) and poor low temperature properties and hence their potential to improve blend properties is limited. This is especially true when blended with low viscosity hydro-processed Group II, Group III fluids or isomerate lubes derived from Fischer-Tropsch wax, which usually have VIs close to or greater than 100. Experience has shown that when Group II, Group III or Fischer-Tropsch wax isomerate fluids are blended with polyisobutylene (PIB) or bright stock, on many occasions, the resulting blends have even lower VIs than the starting Group II or Group III fluids.
High viscosity PAOs have excellent viscometrics and low temperature properties; however, they are more expensive than PIB or bright stock. Moreover, the availability of PAOs is limited to some extent due to the limited supply of the linear alpha olefins, such as 1-decene, used in preparing them.
There is a need, therefore, for fluid lubricant base stocks having good viscometrics, low temperature properties and shear stability that can be made from readily available material.
Accordingly, one object of the present invention is to provide a blend of lubricant fluids having improved viscometrics when compared to blends containing PIB, bright stock or PAOs.
Another object is to provide lubricant fluid blends having improved shear stability when compared to blends containing PIB, bright stock or PAOs.
Other objects and advantages will become apparent upon reading the specification which follows: